Thanks! All sounds a little too easy really! I have just stumbled accross the Park Tools chainline info which actually seems to be making sense. So, from what I can gather from Park, the chainline from the centre of the BB shell to the outside face of the middle ring (using a triple) whould be 50mm, assuming that the rear end has a 50mm chainline? So space it out accordingly on the drive side and match the non drive to it.
Making a bit more sense, but I reckon I am good for at least one balls up fitting it all